Loss of CFTR causes endothelial barrier failure in pneumonia via inhibition of WNK1 and TRPV4 activation

Rationale: Pneumonia is the most common cause of acute respiratory distress syndrome (ARDS). Cystic fibrosis transmembrane conductance regulator (CFTR) is downregulated in infectious and inflammatory conditions. Inhibition of CFTR was found increases lung endothelial permeability in vitro. Objective: We hypothesized that loss of CFTR play role in endothelial barrier failure in pneumonia-induced ARDS, and aimed to elucidate the signaling mechanisms underlying this effect. Methods: CFTR expression was assessed from Streptococcus pneumoniae-infected human and C57/BL6J mice lung tissue. In isolated rat lungs, edema formation, endothelial Cl− ([Cl−]i) and Ca2+ concentration ([Ca2+]i) was quantified by weight gain measurement and real time fluorescence imaging. Lung edema was assessed from S. pneumoniae-infected TRPV4-deficient (trpv4−/-) mice and their wild type (C57/BL6J) controls. Results: CFTR expression decreased in infected human and murine lung. In isolated rat lungs, CFTR inhibition by CFTR-inh172 increased endothelial permeability, [Cl−]i and [Ca2+]i. Inhibition of the Cl− sensitive with no lysine kinase 1 (WNK1) by tyrphostin replicated the effect of CFTR inhibition, while temozolomide, a WNK1 activator, or HC-067047, a TRPV4 antagonist, blocked the CFTR-inh172 effect. In vivo, infected trpv4−/- developed less lung edema and protein leak than their controls. Conclusion:S. pneumoniae infection causes loss of CFTR which promotes endothelial barrier failure through inhibition of WNK1 and subsequent disinhibition of TRPV4, an endothelial Ca2+ channel negatively regulated by WNK1. Inhibition of TRPV4 may present a promising strategy to prevent or treat ARDS in pneumonia patients.